1. Field of the Invention
The present invention relates to means for explosively coupling low-energy detonating cord to a percussion-actuated detonator in an explosive primer. The invention relates also to a primer assembly containing such means for use in the non-electric initiation of cap-insensitive explosives, and more particularly for use in the delayed initiation of deck-loaded explosive charges by means of a single detonating cord downline.
2. Description of the Prior Art
Blasting operations in which a cap-insensitive explosive is to be initiated non-electrically at a delay interval provided in the borehole itself usually require the use of a cap-sensitive high-energy primer (sometimes referred to as a "booster"), a non-electric delay detonator, and a means of operatively connecting the detonator to the primer and to a detonating cord downline. In the deck-loading technique of blasting with such explosives, often used where the elimination of excessive vibration is an important consideration, the cap-insensitive explosive is loaded into the borehole in decks separated from one another by a layer of inert stemming material. When this technique is used, each deck requires a primer (e.g., a primer operatively connected to a detonator), in which the detonator is operatively connected to a downline cord. Systems in which the primers in all of the decks are connected by a single downline are preferred (over those in which an individual downline is required for each primer) because the downline system is less complex and the borehole loading operation and hookup easier.
U.S. Pat. No. 3,709,149, issued Jan. 9, 1973, to H. E. Driscoll, shows a delay booster assembly in which a percussion-actuated delay detonator is seated in a well formed in a cylindrical booster in a direction perpendicular to the longitudinal axis of the cylinder. A detonating cord extends lengthwise of the booster, i.e., perpendicular to the detonator, passing through a loop member at the detonator's actuation end and a cord tunnel member strapped to the booster shell. The detonator is actuated by percussion initiation of an impact-sensitive primer charge caused by the detonation of the cord. In one embodiment, a single downline cord extends through the loop members on the detonators in multiple booster assemblies. One of the disadvantages of the Driscoll booster assembly is that the perpendicular arrangement of the detonator demands a large-diameter booster to accommodate the length of delay detonators commonly used.
In the delay booster assembly described in U.S. Pat. Nos. 4,060,033 and 4,060,034, issued Nov. 29, 1977, to C. Postupack et al. and A. F. Bowman et al., respectively, the non-electric delay detonator is positioned in a cap well which is parallel to the longitudinal axis of the cylindrical booster. Multiple boosters slide on a common 5-6 g/m downline detonating cord threaded through a detonating cord tunnel, affixed to the side of the booster or enclosed inside the booster shell. The cord tunnel is surrounded by a shock-absorbing material. In addition to the downline cord, this system requires the use of a second cord, e.g., a length of low-energy detonating cord (LEDC), with each booster to act as a signal carrier, which transmits a signal from a shock-sensitive sensor to a delay charge in the detonator. The shock-sensitive sensor, attached to one end of the LEDC, is an explosive-containing metal shell positioned with its bottom end adjacent the downline cord. The other end of the LEDC is crimped into the open end of the detonator shell. Thus, this detonator is not a self-contained separate unit adapted for field assembly, but it must be shipped and handled in a delay insert assembly with the shock-sensitive sensor and signal carrier cord, which is housed, for example, in an L-shaped plug that seals the detonator shell.
According to U.S. Pat. No. 4,295,424, issued Oct. 20, 1981, to D. H. Smith et al., the delay detonator in a unit that also includes an initiating means (small primer charge) and a passive radiator (flexible L-shaped hollow tube) should be widely separated from the downline cord, and the passive radiator provides for this separation. The detonator is positioned near the edge of the booster diametrically opposed to the downline cord conduit on the exterior of the booster container.
In a delay booster assembly shown in Austin Technical Data Bulletin ADP 1183, Austin Powder Company, Cleveland, Ohio, entitled, Austin Delay Boosters, the booster container has an external downline channel and an essentially axial delay channel. An elongated delay element, in the form of a delay detonator having the end of a pigtail cord crimped into its shell is used. The detonator is seated in the delay channel and the pigtail inserted into the downline channel. The downline threads through the downline channel, and abuts the pigtail therein, thereby relaying the initiation impulse from the side output of the downline to the detonator.